1. Field of the Invention
The present invention relates to a three-dimensional measurement apparatus in which slit light or pseudo slit light simulatedly created by scanning spot light is irradiated onto an object to form a linear bright portion, the bright portion is detected by image capturing means, and information related to three-dimensional position of the object is obtained from the position of the bright portion in the captured image. The three-dimensional measurement apparatus of the present invention is used as being mounted to a robot, for instance.
2. Description of Related Art
Recently robots have been made more intelligent, whereby in many cases peripheral equipment such as a workpiece supplying and positioning apparatus is simplified. A three-dimensional measurement apparatus that recognizes the three-dimensional position, orientation, shape, size, etc. (hereinafter collectively referred to as “three-dimensional position-related information”) of a workpiece serves as important basic means for intelligent robots. Since the three-dimensional measurement apparatus is often used by being mounted to a robot, the measurement apparatus is demanded not only to have high accuracy but also to be miniaturized.
In the three-dimensional measurement apparatus in which slit light (hereinafter the term “slit light” is a generic name including “pseudo slit light created by spot light scanning”) is irradiated onto a measurement object by using a projector to form a bright portion, light (scattered or reflected light) from the bright portion is detected by a photodetector, and three-dimensional position-related information of the measurement object is measured from the position of the detected bright portion in the detected image, the projector 10 and the photodetector 20 are juxtaposed to each other with a spacing, as shown in FIG. 6a. Thus, the measurement apparatus can be miniaturized by decreasing the installation distance between the projector 10 and the photodetector 20, as shown in FIG. 6b. 
When the measurement apparatus is miniaturized by using such approach, however, the measurement accuracy (especially, the measurement accuracy in the depth direction as seen from the measurement apparatus) is liable to be worsened due to the measurement principle. That is, in the three-dimensional measurement apparatus of the slit light projection type, there are in general conflicting requirements of miniaturizing the apparatus and improving the measurement accuracy. Therefore, and from the viewpoint of compensating demerit due to the miniaturization, the technical art of providing a highly accurate three-dimensional measurement apparatus of the slit light projection type has been strongly demanded.
Under these circumstances, an “object measurement apparatus based on light-section method” has been proposed in JP 8-10130B, for instance. This proposal relates to an object measurement apparatus for measuring the position of a light section line in an image with accuracy higher than the resolution of an image pickup element, and for performing high speed calculation processing to realize a high speed measurement. The apparatus disclosed in JP 8-10130B adopts a method in which a luminance variation in a difference image between an original image and an image observed when slit light is irradiated onto a section line is examined in the direction of each scanning line of a camera, and the center position of the slit light for every scanning line is determined by performing weighted mean processing based on a distribution of luminance that is higher than or equal to a certain threshold.
According to this prior art, however, if a surface portion of a measurement object onto which slit light is irradiated is different in the degree of stain or surface roughness from the remainder, a detected linear bright portion becomes narrow in width or its center position (which indicates the “center position observed when the bright portion is traversed in width direction” (ditto in the following)) is shifted, sometimes resulting in the detected data being largely disturbed. This causes deterioration in the accuracy of detection. Such deterioration becomes more noticeable when the just-mentioned cause and the miniaturization of the measurement apparatus conspire to deteriorate the detection accuracy. Therefore, it is difficult to achieve the miniaturization without causing deterioration in the detection accuracy.